1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring system attached to a vehicle to measure a distance between points and a traveling speed.
2. Description of the Related Art
For example, for creation of an electronic map, a map book and the like, a measuring vehicle called a probe car that photographs geography and buildings, and measures a distance actually travels along roads to collect data. When the measuring vehicle measures a distance between points, a rotary encoder mounted on the outer side of a wheel of the measuring vehicle is used as a conventional measuring apparatus. This rotary encoder incorporates, in a box-like housing, a disk with slits opened at predetermined intervals along a circumferential direction, and a photo interrupter that senses rotation of the slits. This conventional measuring apparatus is mounted by attaching a rotary shaft for rotating the disk to an external center portion of the wheel, and holding the housing by a support which straddles a tire house opened in a fender of a body.
As the rotary encoder, a rotary encoder described in Japanese Utility Model Application Publication No. 5-23775 is known. A rotating device described in the Publication is formed into a cup shape, a rotating member pivotally supported by a rotary shaft of a motor is arranged so as to cover the motor, and another portion of rotation detecting means attached to the rotary member is provided on an inner wall of a container so as to be opposed to a portion of the rotation detecting means. In the rotating device described in the Publication, it is described that the portion of the rotation detecting means is provided as a slit plate, and the other portion configures a photo interrupter made up of a light-emitting element and a light-receiving element, or that the portion of the rotation detecting means is provided as a magnetic signal magnetizing drum with N and S poles alternately arranged, and the other portion is provided as a magnetoresistance element made of permalloy whose resistance varies in accordance with variation in magnetic flux.
However, in the conventional measuring apparatus, the apparatus itself is mounted on the outer side of the wheel, thereby increasing a vehicle width, which may disable the vehicle to enter a narrow path that the vehicle itself could enter. Particularly in a case where the conventional measuring apparatuses are provided on both wheels in order to increase measurement accuracy, the vehicle width further increases.
Moreover, since the rotary shaft of the rotary encoder incorporated in this housing is mounted on the wheel while the housing is mounted on and fixed to the body of the vehicle, in the vehicle in which a shock absorber is arranged obliquely to a car body frame for supporting a wheel hub, the wheel moves up and down in an inclined state in accordance with bumps of a road surface, resulting in that the wheel moves elliptically. Accordingly, in the conventional measuring apparatus, a distance between points and a traveling speed cannot be measured with high accuracy.
Moreover, in the conventional measuring apparatus, since magnetic detection is performed, vibration of the vehicle may also be detected as the rotation of the rotating member, which also makes it difficult to detect the distance between points and the traveling speed with high accuracy.
Consequently, an object of the present invention is to provide a measuring apparatus and a measuring system capable of measuring a distance between points and the like with high accuracy even on a narrow path that a vehicle can enter, and even if there are bumps on a road surface.